However, Mr Sims said he had doubts about parts of NBN Co's new undertaking - especially in relation to pricing.

The government's broadband company submitted the undertaking in December last year, but withdrew it in September after it became clear that it would not be accepted.

Mr Sims said that both the ACCC and NBN believed the new undertaking had "the right overall framework" for regulation, and that "before, there was too much discretion for NBN."

"Most people can get 12 megabits per second services," he said. "We want to make sure that when they transition to NBN, they are not paying any more than they pay now and that price goes down over time."

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Matt Healy, head of regulatory affairs at Macquarie Telecom, said the industry broadly welcomed the ACCC's decision but still needed to resolve some issues.

"There are still real issues to be addressed around how we develop and price new products and who has say over that," Mr Healy said.

"There needs to be crystal clear articulation of when the ACCC can step in and settle disputes between NBN Co and industry."

Also high on Mr Sims' radar is protecting the levels of services to NBN's customers, which will then sell services to millions of Australians.

He asked: "Is the level of service description adequate for the needs of retailers who are going to be selling NBN products to you and I?"

Given the long time-horizon of NBN's project, which will last more than 30 years, the ACCC wants to make sure that there is enough flexibility in the new regulatory system so it can step in to resolve potential future disputes between NBN and its retailer customers.

"You can't anticipate everything over 30 years," Mr Sims said, "have we got the flexibility to deal with new issues as they rise through time."

NBN Co said in a statement that it welcomed the release by the ACCC of its discussion paper as the next stage in the consideration of the Special Access Undertaking.

"NBN Co has pledged to freeze the wholesale price of its key consumer and business products for five years, and to peg any future price rises to below the rate of inflation," NBN Co said in a statement.